1. Field of the Invention
This invention relates to an adhesive based on casein, water-soluble extenders, fillers and optionally other additives and to its use in bottle labeling machines.
2. Discussion of Related Art
Casein adhesives are used as bottle labeling adhesives, primarily in fields where the surfaces to be labeled are wet and cold, i.e. for example in breweries, champagne houses and soft beverage factories. They have acquired a dominant position in these fields because they optimally satisfy the following requirements:
1. Good pumpability and flowability at the application temperature.
2. High wet tackiness for safe label removal.
3. Despite the high wet tackiness, the gripping fingers are able to remove the labels without damaging the constituent paper.
4. When the adhesive is applied to the cold wet surface, part of the water is absorbed by the adhesive, the rest being pushed away during the brushing-on step. Accordingly, the adhesive on the one hand is not overly diluted, on the other hand a continuous film of water is not left beneath the adhesive which, in both cases, would cause the labels to slip. Accordingly, a casein adhesive has an even balance between the absorption of water and the displacement of water. In this way, the casein adhesive immediately establishes firm contact between the label and the surface of the bottle, even a film of water is present on the surface.
5. The casein adhesive provides immediately for firm fixing of the label or foil to the cold wet surface despite the diluting effect of the adhering water. Accordingly, the label does not slip during further processing.
6. At the occasionally very high labeling rates encountered today (up to about 80,000 containers per hour), casein adhesives provide for clean, substantially splash-free processing with no stringing.
7. After drying, a firm bond is established, even to non-reflective glass.
8. Resistance to condensation is sufficient for most requirements.
9. Labels bonded with casein adhesives can readily be removed in good time in modern bottle washing machines using 1.5 to 2.5% sodium hydroxide solution.
Casein adhesives contain approximately 18 to 25% by weight of casein. Casein as a natural product varies to a certain extent in properties so that there is a need to replace casein at least partly with other adhesive substances which, in particular, have safely adjustable and reproducible properties and which are also more economical than casein.
EP B1-0 080 141 describes the production of a casein adhesive and its use for machine labeling. In Example 1, a water-containing adhesive is produced from casein, cornstarch, starch ether and a hydroxyalkyl ether of oxidatively degraded starch and typical additives, such as urea, borax, antifoam agents and preservatives. The adhesive obtained is considerably less temperature-dependent in its viscosity than casein adhesives containing at least 18% of casein.
The present invention seeks to provide a solution to this problem.